Treating molten iron and steel with addition agents



@atented Aug. 8,, i939 UNETE STAT PTENT FIFEQ TREATING MOILTIEN IRON ANDSTEEL WK'EH ADDH'HIQN AGENTS West Virginia No Drawing. Application April14,1938, Serial No. 201,933

8 Claims. (Cl. 75-58) The invention relates to the treatment of molteniron and steel to promote a fine grain structure and freedom fromdeleterious impurities.

During manufacture, steels become contaminated with certain oxides andoccluded gases, which, if not substantially removed or renderedinnocuous, detrimentally affect the soundness and physical properties ofthe finished steel. To

overcome the deleterious effects of such impuri- 10 ties, an addition offerrosilicon or ferromanganese, or both, as deoxidizers, is usually madeto the steel shortly before casting into ingots or other shapes. Forfurther deoxidation, and to provide an inherently fine grainedsteelhaving inhibited grain growth tendencies at elevated temperatures, alater addition of aluminum is often made to the molten steel.

Aluminum additions, in the amounts, for the purposes, and in the mannerdescribed above, tend to produce a steel containing deleterious typesand quantities of non-metallic inclusions. It has been proposed tosubstitute for the aluminum other agents, such as vanadium, zirconium,or titanium, but none of these elements is entirely satisfactory.Vanadium is usually too expensive to add in an amount sufficient toproduce the desired results, and zirconium and titanium as heretoforeused tend to produce a steel containing numerous objectionableimpurities. According to the present invention, a steel that issubstantially free from deleterious gaseous or solid non-metallicimpurities and that has improved mechanical properties (includingimproved impact strength)- and excellent fine grain characteristics isproduced by adding to the steel while it is molten in the ladle orotherwise shortly'before casting, an addition agent containing 25% to85% (preferably to 55%) of silicon, iron; and at least 3% of each of atleast two elements selected from the group vanadium, co-

lumbium, and tantalum. The total amount of the elements selected fromthe group herein described is preferably at least 10% of the compositionof the addition agent. If the number of elements in said mixture is onlytwo, the preferred maximum total amount is 25% of the composition of theaddition agent; and if such number is three, said preferred maximumtotal amount is 30%. Iron is present as an impurity or diluentunavoidably introduced in providing an economical and commerciallypracticable material, and should not exceed about 65%.

The constituents of the addition agent are preferably prealloyed in theform of a master alloy; but they may be unalloyed or only partiallyalloyed, and used in the form of a briquet of comminuted material. Also,some of the constituents thereof may suitably be in the form of easilyreducible or decomposable compounds such as nitrides, nitrates ormixtures thereof. .1 It is essential, however, that the constituents beclosely associated, because successive additions of the severalconstituents separately to the steel do not yield the improved resultsof the invention. 10

In general, the more complex the addition agent, that is, the greaterthe number of deoxidizing ingredients, selected from the above group,the better the results.

In practicing the process of the invention, we 5 prefer to add to themolten steel being treated a sufficient amount of the addition agent ofthe invention that the silicon content of the steel is increased byabout 0.25%. .The deoxidizing or grain refining power may be controlledand 20 varied by adding more or less than enough material to increasethe silicon content of the steels by about 0.25%, or alternatively, theconcentration of silicon relative to the other constituents of theaddition agent may be'varied. If less 25 grain refinement is required,part of the silicon required for deoxidizing may be added as the agentof the invention and part as ordinary ferrosilicon, and if more grainrefinement is required, the action of the addition agent may be 30supplemented by an addition of aluminum or other grain refiner.

The desired composition may be added to the steel in any .well knownmanner, for example, in the furnace, in the ladle, or in the molten 5stream during pouring. When adding the addition agent to the steeleither in the ladle or in the molten stream, an agent containing lessthan about 50% iron should ordinarilybe used in order to minimize thechilling effect of the iron. 40 If the agent is added to the steel inthe furnace, the iron content of the agent may be greater than 50%.

Byproper selection of elements, a grain size of No. 6 or No. '7 mayreadily be procured in steels 45 treated according to a method of theinvention. Throughout the present specification, grain size" refers toaustenitic or inherent grain size determined by the McQuaid-Ehncarburizing test conducted at a temperature of 925 C. for 8 hours, 50 asdefined by the A. S. T. M. specification E 19-33. The degree of grainrefinement or deoxidation of the-steel per unit of addition agent addedwill vary, not only with the combination of elements selected, but alsowith the type of steel being 55 treated, so that the total amount ofagent to be added to the steel for best results must be determined bytrial. Ordinarily, this total'amount of agent will be less than 5%, andmost frequently less than 1%.

While the addition agents of this invention are especially useful in thetreatment of steels which are to be hot worked, the invention is alsoapplicable to the treatment of steels which are to be employed ascastings. Used for the latter purpose, it has been found that, in manyinstances, the characteristics of the casting may be improved if thematerial of the invention is added in an amount which is sufllcient todeoxidize the metal, yet is insufllclent to develop harmful inclusions.

Steels treated according to the invention are sound, substantially freefrom excessive non-metallic inclusions, and possess improved ductilityand shock resistance. Further, the few inclusions distributed throughoutsuch steels are more uniform than diverse, that is, the majority of theinclusions are of the same general type. Undesirable groups or galaxiesof inclusions which usually accompany any deoxidizing treatment thatproduces small grain size are not noticeable in the steels deoxidized inaccordance with the invention until a higher degree of grain refinementis attained than that attainable by the addition of aluminum alone.

We claim:

1. A method of treating molten ferrous metal which comprises adding asmall but effective amount less than 1% of said metal of an additionagent consisting of 25% to 85% silicon, iron, and at least 3% of each ofat least two elements selected from the group vanadium, columbium, andtantalum.

2. A method of treating molten ferrous metal which comprises adding anefiective amount less than 1% of said metal of an addition agentconsisting of 25% to 85% silicon, iron, and 3% to 20% of each of atleast two elements selected from the group vanadium, columbium, andtantalum.

3. A method of treating molten ferrous metal which comprises adding aneifective amount less than 1% of said metal of an addition agentcontaining 35% to 55% silicon; 3% to 20% of each of at least twoelements selected from the group vanadium, columbium, and tantalum, thesum of the elements of said group being at least and not more than 30%;and the remainder iron.

4. A method of treating molten ferrous metal which comprises adding aneffective amount less than 1% of said metal of an addition agentcontaining 35% to 55% silicon; 3% to of at least two elements selectedfrom the group vanadium, columbium, and tantalum; and the remainderiron.

5. A composition of matter, suitable for use as an addition agent fortreating molten ferrous metal, consisting of to 85% silicon, iron, andat least 3% of each of at least two elements selected from the groupvanadium, columbium, and tantalum.

6. A composition of matter for use as an addition agent for treatingmolten ferrous metal, containing 25% to 65% silicon, 3% to 20% of eachof at least two elements selected from the group vanadium, columbium,and tantalum, and the remainder iron.

7. An addition agent for treating molten ferrous metal, containing 35%to 55% silicon, 3% to 20% of each of at least two elements selected fromthe group vanadium, columbium, and tantalum, the sum of the elements ofsaid groups being at .least 10% and not more than and the remainderiron.

8. An addition agent for treating molten ferrous metal, containing to55% silicon, 3% to 20% of at least two elements selected from the groupvanadium, columbium, and tantalum, and the remainder iron.

JAMES H. CRITCHE'I'I. WALTER CRAFTS.

